What is it?
Leg Spring Stiffness (LSS) is a model of elastic energy in the leg, assuming it acts like a spring. It is the maximum vertical force a person generates in a step divided by the displacement during ground contact time.
Why does it matter?
LSS can be a good monitor of changes to running mechanics over time. To compare runs effectively, conditions must be the same (surface, shoe, approximate pace, etc.). It can also be analyzed within training sessions to discern changes in running mechanics within a run, but it is again important to account for show or surface changes within a session.